Campeloma decisum - pointed campeloma

Life History and Reproduction

Campeloma decisum have various truly interesting aspects
regarding their reproduction and their life history. Their
reproduction abilities are extremely diverse among different
populations of the species. Some populations need only one
year to mature, whereas others may need two (Dillon et al., 2006).
Campeloma
decisum are also
ovoviviparous, hence the name of the family that they are
from, Viviparidae (Dillon et al., 2006). The reproduction
diversity is apparent in the fact that some populations of Campeloma decisum are merely parthenogenic
females, and others undergo
outcrossing, and yet there are even other populations
that seem to do a combination of both forms (Dillon et al.,
2006). The
form of reproduction that is most interesting is
parthenogenesis.
Parthenogenesis
Research done by Steven G. Johnson proves that Campeloma decisum do not need
to undergo outcrossing to successfully
carry out parthenogenesis (Johnson, 1992). The origin of
parthenogenesis is believed to be fairly recent due to the clonal variability of the sexual lineages (Johnson, 1992).
The sexual Campeloma decisum lines seem to have different
geographical ranges in comparison to the parthenogenic lines,
with the parthenogens having the larger range (Johnson, 2006).

How is that possible?
Although the parthenogenesis of Campeloma decisum arose
spontaneously, Johnson's 1992 research shows that they continue with
their parthenogenic lifestyle thanks to the trematode species
called Leucochloridiomorpha constantiae. The
metacercariae stage of Leucochloridiomorpha constantiae select
against male Campeloma decisum by limiting sperm. While
sexual populations are not infected with the
metacercariae, the parthenogenic
populations are infected with it in
the brood chamber of females. However,
Leucochloridiomorpha constantiae had to be a part of the
sexual population before it was a part of the parthenogenic
population (since sexual populations developed into
parthenogenic populations). So then how did this
institution of Leucochloridiomorpha constantiae into
sexual populations lead to parthenogenesis? The answer is
quite interesting. When Leucochloridiomorpha
constantiae infected the sexual population, it caused a
sperm limitation which then created a strong selection for
females that were able to reproduce parthenogenically.
This was made possible because the seminal receptacle, where the
sperm is stored, and the
brood chamber, where the egg is stored, of females were right next to each other, making
an easy connection for the metacercariae (Johnson, 1992).

As you can see, the reproduction of Campeloma decisum is not
only very complex, but also quite diverse among different
populations.

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